1. Field of the Invention
This invention relates to fabrics for airbags woven from high decitex per filament multifilament synthetic polymer yarns.
2. Description of Related Art
Fabrics used in airbags should exhibit high strength, low air permeability, and the ability to fold to the least necessary volume. U.S. Pat. No. 5,508,073 (Krummheuer et al.) teaches that advantages in air permeability and specific stiffness are possessed by fabrics made from multifilament polyamide yarns having individual filament fineness of less than five (5) decitex per filament, and more particularly, having individual filament fineness of less than four (4) decitex per filament.
Airbag fabric constructed from blended yarns containing a portion of high decitex per filament yarns and a portion of low decitex per filament yarns are known from published PCT application WO 98-31854 (LaLonde et al.).
The high decitex per filament component is selected from the range of five (5) to fourteen (14) decitex per filament, while the lower linear density per filament yarn is selected from the range of 1.5 to five (5) decitex per filament. The ratio of the components in the LaLonde et al. blended yarn is selected from the range of 1:1 to 1:5 (coarse: fine).
It is believed advantageous to provide a fabric for an airbag made from a multifilament polyamide yarn which takes advantage of the strength inherent in filaments of a high decitex yet which provides the foldability and air permeability performance of filaments with a low decitex.
The present invention is directed to a woven fabric for use in manufacturing an airbag. The fabric is made from a plurality synthetic polymer multifilament yarns extending in substantially perpendicular warp and weft directions. Each multifilament yarn comprises a plurality of individual filaments with each individual filament having a linear density in the range from about eight (8) decitex to about eleven (11) decitex per filament, and more preferably, a linear density in the range from about nine (9) decitex to about eleven (11) decitex per filament. The fabric has a circular bend stiffness in the range of about four (4) Newtons to about seven (7) Newtons, as measured in accordance with ASTM method D4032-94.
Preferably, the multifilament yarns have a linear density (yarn titer) in the range from about two hundred (200) to about six hundred (600) decitex, and more preferably, in the range from about two hundred fifty (250) decitex to about five hundred fifty (550) decitex.
Such multifilament yarns are woven in substantially perpendicular warp direction and weft directions, as in a plain weave fabric. The typical fabric sett is from eighteen (18) to twenty-five (25) yarns per centimeter in either warp or weft directions. Fabrics of this type have a circular bend stiffness, also known as xe2x80x9cKingxe2x80x9d stiffness, of 0.9 pounds of force (four Newtons) to about 1.6 pounds of force (7.1 Newtons) as measured according to ASTM method D4032-94. Fabrics constructed from the preferred yarns have an areal density of about one hundred twenty-five (125) grams per square meter to about two hundred fifty (250) grams per square meter.
Fabrics made of heavy decitex per filament yarns in accordance with the present invention provide airbags that are lighter in weight and have improved foldability as measured by circular bend stiffness, the fabric""s resistance to circular bending.
Suitable synthetic polymers from which preferred high decitex filament yarns are prepared include: nylon 66, nylon 6, nylon 46, nylon 12, nylon 612, and polyesters like 2GT, 2GN, 3GN and 3GT. Nylon 66 is an especially preferred polymer for the high decitex multifilament yarns in accordance with the present invention.